What was the original etching method used in early IC manufacturing, and what limits it?	Wet chemical etching — it is isotropic (etches in all directions equally), which undercuts fine features and is unusable at modern dimensions.
What gas chemistry is used in plasma etching for silicon and silicon oxides?	Fluorine compounds (e.g., SF₆, CF₄).
What gas chemistry is used for plasma etching of metals?	Chlorine compounds.
What volatile compound does silicon form when plasma-etched with fluorine?	Silicon tetrafluoride (SiF₄), which pumps away as a gas.
What does 'etch selectivity' mean?	The ratio of etch rate on the target material to the etch rate on the masking material; optimized recipes approach 1,000:1.
What makes RIE anisotropic?	Positive ions are accelerated downward by an RF bias, striking the surface vertically and driving the etch straight down rather than laterally.
What do boron dopants contribute electrically to silicon?	Holes — positive charge carriers — making the silicon P-type.
What do phosphorus or arsenic dopants contribute?	Free electrons, making the silicon N-type.
What energy range is typical for ion implantation?	Tens of thousands of volts (tens of keV) — around ~50 keV typically.
To what temperature is the wafer heated during a rapid thermal anneal?	Around 1,000°C, sometimes up to 1,200°C, for seconds at a time.